IDO1 and neoplasm: However, IDO1 expression positively correlated with lymph node metastasis, pleural invasion, tumor recurrence, lower tumor differentiation, solid tumor components, preoperative chemotherapy, and clinical tumor, node, metastasis (TNM) staging (*<i>P</i> < 0.05), while negatively correlating with prior surgical history (*<i>P</i> < 0.05).